# Solar light CdS cell repair

#### wayneh

Joined Sep 9, 2010
16,114
I was setting out my Christmas-themed solar lights today and was disappointed to see than half have failed because they won't shut off in the light. One of the failed units will just shut off if I hold it against the light bulb. The working units shut off with just ambient room light.

Anyway, these all have a little CdS cell in them, about 3/16" in diameter. They aren't perfectly sealed against water (snow) and that's why they get corroded and fail. I'm pretty sure a replacement cell would get these lights working.

Question: Do I need to worry about any CdS cell specification other than physical size?

Secondary question: Know where to get these cheap?

Joined Jan 15, 2015
4,573
Question: Do I need to worry about any CdS cell specification other than physical size?

Secondary question: Know where to get these cheap?
Yes, as Dick mentioned you need some idea of the Light/Dark resistances.

Every now and then I have added a bunch with my wife's Amazon orders. Something like these where there are 30 pieces of pretty common ones for just over $5 USD,Again, you at least need to know the Light / Dark resistances. Sometimes you can get a package of "assorted" for a few bucks. Unfortunately the bargain basement stuff like I linked to does not always have a data sheet or even a part number to work from. Ron Thread Starter #### wayneh Joined Sep 9, 2010 16,114 Yes, as Dick mentioned you need some idea of the Light/Dark resistances. Every now and then I have added a bunch with my wife's Amazon orders. Something like these where there are 30 pieces of pretty common ones for just over$5 USD,Again, you at least need to know the Light / Dark resistances. Sometimes you can get a package of "assorted" for a few bucks. Unfortunately the bargain basement stuff like I linked to does not always have a data sheet or even a part number to work from.

Ron
That's exactly what I just ordered! I'll have them by Friday. I was tempted by these (I'm a sucker for a bargain) but I resisted. The tip in was that some of the customer reviews noted successful repairs of solar lights. Worth a shot.

#### wayneh

Joined Sep 9, 2010
16,114
Success! Today I finally got around to making my repairs and had a 4-for-4 success rate. The CdS cells from Amazon fit and worked perfectly. They turn the LED on/off at a very low light level, probably less light than the other original ones. That may be aging of the original CdS cells or just different behavior of the new cells but anyway switching at a darker level works in favor of sparing the batteries.

It's satisfying to move these Xmas lights from the junk pile to active duty, but I cannot recommend this repair for average solar lights. It's satisfying but I mean, they give these things away for free. It took me the morning to do the teardowns, soldering and hot gluing to get these 4 lights back in service. If they weren't unique as a Xmas decoration, it wouldn't have been worth the effort.

For what it's worth, my lights look a bit like these:

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